This proposal investigates the neural basis of orientation and form perception by a non-vertebrate model system, the dipteran Phaenicia sericata. The research will identify visual parameters pertinent to low-level form vision using behavioral tests. It will then employ these parameters as stimuli for testing the filter properties of identified neurons in a neuropil having neuroanatomical characteristics analogous to mammalian visual cortex. To understand mechanisms of visual perception, investigations at the single cell level must be performed against a background of detailed morphological analysis such that the structure of single neurons responding to specific visual stimuli can be related to the overall neuroanatomical context of the system. The dipteran compound eye and optic lobes offer an ideal substrate for such an investigation. The optic lobes' succession of retinotopically organized neuropils is functionally analogous to organization amongst mammalian visual regions, but contains orders of magnitude fewer neurons. In particular, the planned research will focus on the lobula, a neuropil supplied by the parvicellular element of this visual system and containing within it nerve cells that are structurally analogous to pyramidal and stellate neurons of mammalian cortex. The relative simplicity of this model system facilitates the identification of single computational units and allows detailed circuit analysis A further advantage of this simple system is that it reflects evolutionarily conserved principles of visual system design that cut across phylogenetic boundaries. The proposed will investigate: . the ability of a dipteran species to discriminate visual patterns and shapes containing orientation and texture information. . the cellular properties of neurons and circuits in the lobula that discriminate orientations and textures. . the anatomical organization of pyramidal-like and stellate-like neurons in the dipteran lobula.